<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>商城</title>
    <style>
        #d1{ width: 900px; height: 600px; border: 1px red dashed; 
            margin: 0 auto;}
        #top{
            width: 900px;
            height: 120px;
            background-color: aquamarine;
        }    
    </style>
</head>
<body>
   <div id="d1">
      <div id="top">欢迎来到商城</div>
      <div id="center"></div>
   </div>    
</body>
</html>